1. Field of the Invention
The present invention relates generally to devices for the generation and amplification of electromagnetic energy. The present invention relates more particularly to optical fiber devices, such as lasers and amplifiers, useful for generating and amplifying optical energy.
2. Technical Background
Optical fiber lasers and amplifiers are known in the art. In such lasers and amplifiers, rare earth materials disposed in the core of the optical fiber therein absorb pump radiation of a predetermined wavelength, and, in response thereto, provide or amplify light of a different wavelength for propagation in the core. For example, the well-known erbium doped fiber amplifier receives pump radiation having a wavelength of 980 or 1480 nm, and amplifies an optical signal propagating in the core and having a wavelength of about 1550 nm.
In such optical fiber lasers and amplifiers, the pump radiation can be introduced directly to the core, which can be difficult due to the small size of the core, or can be introduced to the cladding layer surrounding the core and absorbed by the core as the rays propagating in the cladding layer intersect the core. Lasers and amplifiers in which the pump radiation is to be introduced to the cladding layer are known as “cladding pumped” optical devices. Cladding pumping can facilitate the scale-up of lasers and amplifiers to higher power systems.
One complication is that cooperative effects that can cause excess loss, increase noise, or even damage the optical fiber. Accordingly, in certain applications, it can be desirable to minimize up-conversion and luminescence in rare earth doped fiber devices, as they can tend to limit the gain achievable by the device, decrease pumping efficiency, and increase noise to unacceptable levels.
Accordingly, there remains a need in the art for optical fiber devices, such as lasers and amplifiers, that provide acceptable gain and efficiency and suffer relatively less from these cooperative effects.